Broadway comes to the opera as theater vets Brance Cornelius and Lauren Hoffmeier sparkle in Dicapo’s take on Frank Loesser.James Martindale

A gloomy, middle-aged immigrant becomes “The Most Happy Fella” in Frank Loesser’s much-loved 1956 musical. But the audience for the Dicapo Opera’s spunky new revival has plenty to be happy about, too.

This gentle romance between Tony, an aging Italian-American vineyard owner, and Rosabella, a young waitress, is a departure for Loesser, best known for jazzy shows like “Guys and Dolls” and “How To Succeed in Business Without Really Trying.”

But so bountiful is his score for “Fella” — ranging from hit parade-ready tunes like “Standing on the Corner” to throbbing arias such as “My Heart Is So Full of You” — that it’s crossed over to venues like the New York City Opera.

True to the show’s pedigree, Dicapo performs it “acoustic”-style — without microphones. And the best part of this approach is how good the 32-piece orchestra sounds under Pacien Mazzagatti, its golden tone making modern Broadway pit bands sound like kazoos.

As far as the vocals go, the Dicapo regulars are upstaged by the cast’s two musical-theater ringers. Lauren Hoffmeier as the sassy waitress Cleo is a throwback to brass-lunged divas like Ethel Merman, with an alto belt that can stun at 20 paces.

She’s matched by Brance Cornelius as her timid boyfriend, Herman. His penetrating tenor and bouncy comic energy kicked the second act into high gear with the Western-flavored “Big D.”

Baritone Timothy Lafontaine soared easily through the long role of Tony, even if his radiant smile and dapper presence made Rosabella’s initial rejection seem ridiculous: How could she possibly prefer his rival, the foreman Joe, as performed by the tubby, small-voiced Peter Kendall Clark?

As Rosabella, Molly Mustonen was a little short on spunk, and her sweet soprano took on an edge in Dicapo’s dry acoustic. A worse letdown was Michael Capasso’s direction: rudimentary blocking among a few sticks of furniture, with only Hoffmeier and Cornelius supplying the requisite razzle-dazzle.

Even so, this “Fella” is a keeper, both as a reminder of how Broadway used to be and a lesson that an opera company doesn’t have to be big to be important.